Solvent-dependent deuterium isotope effects in the 15N NMR spectra of an ammonium ion

Deuterium isotope effects on N-15 NMR chemical shifts and spin-spin coupling constants have been investigated for the N-15-enriched ammonium chloride(conc. < 0.1 M) in liquid solutions, The (NH4)-N-15' ion has been observed in water, methanol, ethanol and dimethylsulfoxide, while the (ND4)-N-15' has been monitored in the analogous deuterated liquids. It is shown that the isotope effect in nitrogen chemical shifts ((1)Delta(15)N(H-2/1)), significantly different in various solvents, changes from -1.392 ppm in dimethylsulfoxide to -0.071 ppm in ethanol. The (1)J(N,H) and (1)J(N,D) coupling constants have been measured for acidic solutions under conditions of slow proton (or deuterium) exchange. The reduced coupling constants have been estimated to present isotope effects in the spin-spin coupling constants. The latter isotope effects are fairly small.